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At least 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Ultrasonic determination of thermodynamic threshold parameters for irreversible cutaneous burns

In vivo ultrasonic measurements of the depth of conductive cutaneous burns experimentally induced in anesthetized Yorkshire pigs are reported as a function of burn time for the case in which the skin surface temperature is maintained at 100 C. The data are used in the solution of the one-dimensional heat diffusion equation with time-dependent boundary conditions to obtain the threshold temperature and the energy of transformation per unit mass associated with the transition of the tissue from the state of viability to the state of necrosis. The simplicity of the mathematical model and the expediency of the ultrasonic measurements in studies of thermal injury are emphasized.

Cantrell, J. H., Jr.↗
NASA NTRS1982

Heat generation in aircraft tires under free rolling conditions

A method was developed for calculating the internal temperature distribution in an aircraft tire while free rolling under load. The method uses an approximate stress analysis of each point in the tire as it rolls through the contact patch, and from this stress change the mechanical work done on each volume element may be obtained and converted into a heat release rate through a knowledge of material characteristics. The tire cross-section is then considered as a body with internal heat generation, and the diffusion equation is solved numerically with appropriate boundary conditions of the wheel and runway surface. Comparison with data obtained with buried thermocouples in tires shows good agreement.

Clark, S. K.↗
NASA NTRS1983

Heat generation in aircraft tires

A method was developed for calculating the internal temperature distribution in an aircraft tire while free rolling under load. The method uses an approximate stress analysis of each point in the tire as it rolls through the contact patch, and from this stress change the mechanical work done on each volume element may be obtained and converted into a heat release rate through a knowledge of material characteristics. The tire cross-section is then considered as a body with internal heat generation, and the diffusion equation is solved numerically with appropriate boundary conditions of the wheel and runway surface. Comparison with data obtained with buried thermocouples in tires shows good agreement.

Clark, S. K.↗
NASA NTRS1981

An empirical investigation of methods for nonsymmetric linear systems

The present investigation is concerned with a comparison of methods for solving linear algebraic systems which arise from finite difference discretizations of the elliptic convection-diffusion equation in a planar region Omega with Dirichlet boundary conditions. Such linear systems are typically of the form Ax = b where A is an N x N sparse nonsymmetric matrix. In a discussion of discretizations, it is assumed that a regular rectilinear mesh of width h has been imposed on Omega. The discretizations considered include central differences, upstream differences, and modified upstream differences. Six methods for solving Ax = b are considered. Three variants of Gaussian elimination have been chosen as representatives of state-of-the-art software for direct methods under different assumptions about pivoting. Three iterative methods are also included.

Sherman, A. H.↗
NASA NTRS1983

Turbulent heating in solar cosmic ray theory

The heating of minor ions in solar flares by wave-wave-particle interaction with Langmuir waves, or ion acoustic waves, can be described by a diffusion equation in velocity-space for the particle distribution function. The dependence of the heating on the ion charge and mass, and on the composition of the plasma, is examined in detail. It is found that the heating mechanisms proposed by Ibragimov and Kocharov cannot account for the enhanced abundances of heavy elements in the solar cosmic rays.

Weatherall, J.↗
NASA NTRS1984

Turbulent heating in solar cosmic-ray theory

The heating of minor ions in solar flares by wave-wave-particle interaction with Langmuir waves, or ion acoustic waves, can be described by a diffusion equation in velocity-space for the particle distribution function. The dependence of the heating on the ion charge and mass, and on the composition of the plasma, is examined in detail. It is found that the heat mechanisms proposed by Ibragimov and Kocharov cannot account for the enhanced abundances of heavy elements in the solar cosmic rays.

Weatherall, J.↗
NASA NTRS1985

On the structure of the turbulent vortex

The trailing vortex generated by a lifting surface, the structure of its turbulent core and the influence of axial flow within the vortex on its initial persistence and on its subsequent decay are described. Similarity solutions of the turbulent diffusion equation are given in closed form and results are expressed in sufficiently simple terms that the influence of the lifting surface parameters on the length of persistence and the rate of decay of the vortex can be evaluated.

Roberts, L.↗
NASA NTRS1985

Propagation and secondary production of low energy antiprotons in the atmosphere

Current theories, in which the observed antiproton component is attributed strictly to secondary production in high energy inelastic collisions of protons with the interstellar medium or the atmosphere, apparently fail to explain the relatively high p vertical intensities measured at mountain and balloon altitudes. Therefore, a more careful calculation of the theoretical secondary intensity spectra is required before more exotic sources for these excess p's can be explored. A one dimensional diffusion equation is used to calculate the expected vertical intensity of p's due only to secondary production in the atmosphere; any assumed primary p spectrum is also included. Two adjustable parameters, the inelasticity and charge exchange in nucleon-nucleus collisions, were included in the algorithm. In order to obtain an independent estimate of their values the proton vertical intensities in the atmosphere were calculated, adjusting the parameters until the curves fit the experimental proton data, and then assumed that these values were identical in antinucleon-nucleus collisions.

Bowen, T.↗
NASA NTRS1985

Spatial distribution of cosmic rays in magnetic cycles of the Sun

The space-time distribution of cosmic ray (CR) density is determined from the solution of the anisotropic diffusion equation. The boundary problem is solved in a quasistationary axisymmetric case, taking into account the delay of cosmic rays relative to the cyclic variations of solar activity. The specificty of the modulation model is the use of the empirical dependence of the free path of particles for scattering on the observed latitudinal distribution of solar activity. Another specific feature of the model is an account of an additional effect due to the drift of charged particles towards the helio-equator plane or backward, depending on the direction of the total magnetic field of the Sun.

Alania, M. V.↗
NASA NTRS1985

Diffusion of strongly magnetized cosmic ray particles in a turbulent medium

Cosmic ray (CR) propagation in a turbulent medium is usually considered in the diffusion approximation. Here, the diffusion equation is obtained for strongly magnetized particles in the general form. The influence of a large-scale random magnetic field on CR propagation in interstellar medium is discussed. Cosmic rays are assumed to propagate in a medium with a regular field H and an ensemble of random MHD waves. The energy density of waves on scales smaller than the free path 1 of CR particles is small. The collision integral of the general form which describes interaction between relativistic particles and waves in the quasilinear approximation is used.

Ptuskin, V. S.↗
NASA NTRS1985

The theoretical and experimental investigation of cosmic ray Forbush-effects

The theoretical results of analysis of the expected spatial distributions of density, gradients and anisotropy of cosmic rays, obtained on the basis of the numerical solution of anisotropic diffusion equation in the presence of the disturbances of shock wave type in the interplanetary space are presented. The theoretical calculations on the definition of the energy spectrum and anisotropy of galactic cosmic rays during Forbush effect are compared with the experimental data.

Alania, M. V.↗
NASA NTRS1985

Neutrino production from the solar atmosphere

When the high energy primary cosmic rays enter near the solar surface, they pass through a thick matter but having a low density. If the density and path length satisfy an appropriate condition, the primaries collide with the constituents near the solar sphere (almost protons) and produce pions and kaons, most of which decay into mu plus nu sub mu without successive hadron collisions. Muons also decay into NU sub mu and NU sub e before reaching the Earth. The neutrino flux of which the producer is matter near the solar surface is computed by solving cascade diffusion equations. The calculated differential flux of muon neutrino at 1 TeV is 1 X 10 to the minus 13 power (GeV. cm square centimeters 2.s.ster)(-1) which is rather difficult to be observed in the present apparatuses or DUMAND.

Inazawa, H.↗
NASA NTRS1985

The nucleon intensity in the atmosphere and the Pt distribution

The diffusion equation for cosmic ray nucleons in the atmosphere has been solved analytically, taking into account the transverse momentum distribution of nucleons produced in nucleon-air nucleus collisions. The effect of the transverse momentum distribution increases the nucleon intensity at large zenith angles and low energies.

Liland, A.↗
NASA NTRS1985

Comparison of big event with calculations of the air shower development

The incidence of high energy hadrons and electron-photons in air showers at various stages of development is calculated. Numerical calculation is used to solve the diffusion equation for a nuclear cascade and analytical calculation for cascade shower induced gamma rays. From these calculations, one can get the longitudinal development of the high energy hadron and electron-photon components, and the energy spectra of these components at various depths of air shower development. The total number of hadrons (N sub H) and electron-photon components (N sub gamma) are related according to stages of the air shower development and primary energy. The relation of the total energy of hadron and electron-photon component above the threshold energy is given. The energy balance between both components is also a useful parameter to study high energy events accompanying air showers. The relation of N sub H and fractional hadronic energy E (sum E sub H sup gamma/sum E sub H sup gamma + Sum E sub gamma) is calculated. This relation is helpful to understand the stage of air shower development(t) and primary energy (E sub p).

Niwa, M.↗
NASA NTRS1985

Energy spectra of high energy atmospheric neutrinos

Focusing on high energy neutrinos ( or = 1 TeV), a new calculation of atmospheric neutrino intensities was carried out taking into account EMC effects observed in P-A collisions by accelerator, recent measurement of primary cosmic ray spectrum and results of cosmic ray muon spectrum and charge ratio. Other features of the present calculation are (1) taking into account kinematics of three body decays of kaons and charm particles in diffusion equations and (2) taking into account energy dependence of kaon production.

Mitsui, K.↗
NASA NTRS1985

Atmospheric muons and neutrinos, and the neutrino-induced muon flux underground

The diffusion equation for neutrino-induced cosmic ray muons underground was solved. The neutrino-induced muon flux and charge ratio underground have been calculated. The calculated horizontal neutrino-induced muon flux in the energy range 0.1 - 10000 GeV is in agreement with the measured horizontal flux. The calculated vertical flux above 2 GeV is in agreement with the measured vertical flux. The average charge ratio of neutrino-induced muons underground was found to be mu+/mu- = 0.40.

Liland, A.↗
NASA NTRS1984

An improved thermal model for cometary nuclei

A thermal model for cometary nuclei is presented and used in comparisons of predictions with data on Halley's comet. The model considers the surface boundary conditions and heat diffusion equations, the sublimation rate of ice, the energy balance, and the dust production rate. Projections were made for the Halley nucleus over 18 latitudes from -85 to +85 deg, from 185 d before to 110 d after perihelion, and in 20 layers of its surface in 1.3 cm increments. Sublimation is predicted to increase by a factor of 2.2 every orbit, thereby allowing 320 returns for a nucleus with a coma, 710 returns with a bare ice nucleus. The gas production during the Giotto intercept at 0.9 AU will be 4.4 x 10 to the 29th molecules/sec, close to an estimate made during the 1910 return.

Weissman, P. R.↗